Noise quieting with random PWM AC drives

Acoustic noise radiated by industrial drives driven by PWM power electronic controllers is becoming ever more objectionable on industrial sites. The authors investigate such noise and show that the noise spectrum is closely related to the spectrum of the voltage waveform formed by the power electronics so that it may be ‘controlled’ by controlling the voltage waveform. The paper describes a random PWM modulator and shows how it may be tailored within a prescribed band of switching frequencies to ‘smear’ the voltage spectrum. Measured spectra and the results of listening tests are presented to show that significant perceived noise reductions are possible for relatively low switching bandwidths with but small computational overheads in the PWM generation.